Black perylene pigment and process for producing the same

ABSTRACT

A black perylene-based pigment produced by calcining at least one compound selected from the group consisting of diimide derivatives of perylene tetracarboxylic acid and diimide derivatives of perylene diiminodicarboxylic acid, at a temperature of 200 to 600° C. in vacuum or in an inert gas atmosphere, exhibits an excellent blackness, an excellent heat resistance and an excellent weather fastness as well as a high resistance and a high safety.

TECHNICAL FIELD

The present invention relates to a black perylene-based pigment and aprocess for producing the same, and more particularly, to a blackperylene-based pigment having a high blackness, a high tinctorialstrength, an excellent heat resistance and an excellent weather fastnessas well as a high safety and a high electrical resistance, and a processfor producing such a black perylene-based pigment. The blackperylene-based pigment of the present invention is useful as coloringpigments for inks, paints, ink-jet printing inks, electrophotographictoners, rubbers and plastics, black matrix pigments for liquid crystalcolor filters, etc.

BACKGROUND ART

As black pigments, there have been conventionally used carbon black,perylene-based pigments and the like. Among these black pigments, carbonblack has been most widely used because of its high tinctorial strengthas well as an excellent blackness, an excellent acid resistance and anexcellent weather fastness. However, carbon black has a very smallparticle size and a large bulk density and, therefore, tends to sufferfrom problems such as poor handling property and workability. Also, itmay be difficult to use such carbon black in applications requiring ahigh electrical resistance, such as black matrix materials for liquidcrystal color filters, because of a low electrical resistance thereof.Further, the carbon black may contain carcinogenic polycycliccondensation compounds and, therefore, has a problem concerning asafety.

Although the perylene-based pigments extensively used as fast pigmentsexhibit red-violet-brown-black colors in a solid state, the color tonethereof is not necessarily kept thermally stable (W. Herbst & K. Hunger“Industrial Organic Pigments”, VCH Press, pp. 467-480).

An object of the present invention is to provide a black perylene-basedpigment exhibiting an excellent blackness, an excellent heat resistanceand an excellent weather fastness as well as a high safety, which isusable as black matrix pigments for liquid crystal color filters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing an X-ray diffraction diagram of the blackpigment obtained in Example 1.

FIG. 2 is a graph showing a light absorption spectrum of the blackpigment obtained in Example 1.

DISCLOSURE OF THE INVENTION

The above object of the present invention can be accomplished by a blackperylene-based pigment obtained by using calcining techniques which havenot been conventionally used in the application field of organicpigments, and more specifically by calcining a specific perylene-basedpigment at a specific temperature.

In an aspect of the present invention, there is provided a blackperylene-based pigment produced by calcining at least one compoundselected from the group consisting of compounds represented by thefollowing formulae (I) to (III), at a temperature of 200 to 600° C. invacuum or in an inert gas atmosphere.

wherein R¹ and R² are identical to each other and are independentlybutyl group, phenylethyl group, methoxyethyl group and4-methoxyphenylmethyl group; and R³ and R⁴ may be same or different andare independently phenylene group, alkylphenylene group, alkoxyphenylenegroup, hydroxyphenylene group, halogenated phenylene group, pyridinediylgroup, alkylpyridinediyl group, alkoxypyridinediyl group, halogenatedpyridinediyl group and naphthalenediyl group, the said R³ and R⁴ beingbonded to adjacent positions of the aromatic ring, respectively.

In another aspect of the present invention, there is provided a processfor producing a black perylene-based pigment, which comprises the stepof calcining at least one compound selected from the group consisting ofthe compounds represented by the above formulae (I) to (III) at atemperature of 200 to 600° C. in vacuum or in an inert gas atmosphere.

The present invention is described in detail below. The blackperylene-based pigment of the present invention is produced by calciningat least one compound selected from the group consisting of thecompounds represented by the formulae (I) to (III) at a temperature of200 to 600° C. in vacuum or in an inert gas atmosphere. The blackperylene-based pigment obtained by the above calcining treatment canexhibit a good thermally stability and a suitable change in moleculararrangement from that of the raw compound. The thermal stability of theblack perylene-based pigment can be confirmed as follows. That is, thehue values of the pigment heat-treated in an oven at 200° C. for onehour and the non-heat-treated pigment are measured, and a colordifference (ΔE) therebetween is calculated from the measured values. Inthe case where the color difference (ΔE) is not more than 0.3, it isdetermined that the pigment has a good thermal stability. Also, thechange in molecular arrangement can be confirmed by determining that thecalcined pigment exhibits an X-ray diffraction pattern different fromthat of the non-calcined pigment.

Examples of the R¹ and R² groups of the compounds represented by theformula (I) may include butyl group, phenylethyl group, methoxyethylgroup and 4-methoxyphenylmethyl group.

Examples of the preferred R³ and R⁴ groups of the compounds representedby the formulae (II) and (III) may include phenylene group,3-methxoyphenylene group, 4-methoxyphenylene group, 4-ethoxyphenylenegroup, C₁ to C₃ alkylphenylene group, hydroxyphenylene group, 4,6-dimethylphenylene group, 3,5-dimethylphenylene group, 3-chlorophenylenegroup, 4-chlorophenylene group, 5-chlorophenylene group,3-bromophenylene group, 4-bromophenylene group, 5-bromophenylene group,3-fluorophenylene group, 4-fluorophenylene group, 5-fluorophenylenegroup, 2,3-pyridinediyl group, 3,4-pyridinediyl group,4-methyl-2,3-pyridinediyl group, 5-methyl-2,3-pyridinediyl group,6-methyl-2,3-pyridinediyl group, 5-methyl-3,4-pyridinediyl group,4-methoxy-2,3-pyridinediyl group, 4-chloro-2,3-pyridinediyl group andnaphthalenediyl group.

Among these R³ and R⁴ groups, more preferred are phenylene group,2,3-pyridinediyl group and 3,4-pyridinediyl group.

Next, the process for producing the black perylene-based pigmentaccording to the present invention is described below. According to theprocess of the present invention, at least one compound selected fromthe group consisting of the compounds represented by the formulae (I) to(III) is calcined in vacuum or in an inert gas atmosphere at atemperature of usually 200 to 600° C., preferably 450 to 550° C. forusually 0.5 to 2 hours, preferably 1 to 2 hours. As the inert gas, theremay be used helium, argon or the like. The resultant calcined product issubjected to ordinary finishing treatments such as milling, therebyobtaining fine perylene-based pigment.

As described above, the fine perylene-based pigment is produced bycalcining the perylene derivative. By conducting the calcining treatmentat a temperature of 200 to 600° C., the obtained pigment can beincreased in its blackness. The reason why the blackness of the pigmentis increased by such a calcining treatment, is considered as follows.That is, according to Jin Mizuguchi, “Organic Pigments and TheirElectron Structure”, Journal of Japan Imaging Society, Vol. 37, pp.256-257 (1998) relating to color change due to resonance interactionbetween excited molecules, the position and intensity of the absorptionband considerably varies depending upon change in resonance interactionbetween excited molecules, which is caused by the change in moleculararrangement. Accordingly, it is considered that as a result of changingthe molecular arrangement of the fine perylene-based pigment byconducting the calcining treatment at the above-specified temperature,the change in resonance interaction between excited molecules is caused,so that the fine perylene-based pigment shows an absorption bandcovering a whole visible light region, resulting in increased blacknessthereof.

The thus obtained black perylene-based pigment exhibits an excellentblackness, an excellent heat resistance and an excellent weatherfastness as well as a high electrical resistance and a high safety and,therefore, is useful as coloring pigments for inks, paints, ink-jetprinting inks, electrophotographic toners, rubbers and plastics, andpigments for black matrix materials.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in more detail by Examples, but theExamples are only illustrative and, therefore, not intended to limit thescope of the present invention.

(1) Blackness:

The blackness of the black perylene-based pigment was expressed by theratio of a minimum value to a maximum value of an absorption band in avisible light region (refer to FIG. 2). When the ratio is not less than0.55, the obtained black pigment showed a high blackness. The ratio ofthe minimum value to the maximum value of the absorption band ispreferably not less than 0.65, more preferably not less than 0.75. Thevisible light absorption spectrum of a test specimen was measured by aspectrophotometer “UV-2400PC” (manufactured by SHIMADZU SEISAKUSHO CO.,LTD.), thereby obtaining the minimum value and the maximum value ofabsorption band thereof. Meanwhile, the test specimen used for themeasurement of the visible light absorption spectrum was prepared asfollows. That is, 0.1 g of the black perylene-based pigment and 0.5 mlof castor oil were mixed together by a Hoover's muller to produce apaste. 4.5 g of clear lacquer was added to the obtained paste and wasintimately kneaded to produce a paint. The obtained paint was applied onan OHP sheet by using a 1-mil applicator, thereby obtaining a coatingfilm thereon.

(2) Tinctorial Strength:

The tinctorial strength, the weather fastness and the heat resistance ofthe black perylene-based pigment were evaluated by using L*, a* and b*values according to CIE space, i.e., uniform sensory color space ofCommission Internationale de l'Eclairage (1976). The tinctorial strengthwas determined as follows. That is, the L* value of a specimen wasmeasured by using a spectrocolorimeter “Color Guide” (manufactured byBYK-Gardner GmbH), and the visual reflectivity Y (%) was calculated fromthe measured L* value according to the following formula:Y (%)=L* ²/100

Further, the Munsell value V was obtained from the thus calculatedvisual reflectivity Y value by referring to Attached Table-2 ofJIS-Z-8721.

The tinctorial strength (TS (%)) of a test specimen was calculated fromthe Munsell value (VA) of a control specimen and the Munsell value (VB)of the test specimen according to the following formula:TS (%)={1−(VB−VA)}×100

The test specimen was prepared as follows. That is, 0.5 g of the blackperylene-based pigment, 1.5 g of titanium oxide and 0.5 ml of castor oilwere mixed together by a Hoover's muller to form a paste. 4.5 g of clearlacquer was added to the obtained paste and was intimately kneaded toform a paint. The obtained paint was applied on a cast-coated paper byusing a 6-mil applicator, thereby obtaining a coating film thereon. Thecontrol specimen was prepared as follows. That is, 0.5 g of the blackperylene-based pigment obtained in Comparative Example 1, 1.5 g oftitanium dioxide and 0.5 ml of castor oil were mixed together by aHoover's muller to form a paste. 4.5 g of clear lacquer was added to theobtained paste and was intimately kneaded to form a paint. The obtainedpaint was applied on a cast-coated paper by using a 6-mil applicator,thereby obtaining a coating film thereon.

(3) Weather Fastness:

The black perylene-based pigment particles were placed about 10 cmunderneath an ultra-high pressure mercury lamp (500 W, manufactured byUSHIO DENKI CO., LTD.) and irradiated with light therefrom for 8 hours.The thus irradiate-treated black perylene-based pigment particles aswell as non-irradiate-treated black perylene-based pigment particleswere used to prepare each of test specimens by the below-mentionedmethod. The L*, a* and b* values of the test specimens were measured,and the weather fastness of the black perylene-based pigment particleswas expressed by the color difference (ΔE) calculated from the measuredL*, a* and b* values according to the following formula:ΔE={square root}{square root over ((L _(s) −L)²−(a _(s) −a)²+(b _(s)−b)²)}wherein L_(s)*, a_(s)* and b_(s)* represent hue values of thenon-treated black perylene-based pigment; and L*, a* and b* representhue values of the treated black perylene-based pigment.

When the color difference (ΔE) is not more than 0.3, the obtained blackperylene-based pigment was free from change in hue between before andafter the treatment and, therefore, had an excellent weather fastness.

The test specimens were prepared as follows. That is, 0.5 g of the blackperylene-based pigment and 0.5 ml of castor oil were mixed together by aHoover's muller to form a paste. 4.5 g of clear lacquer was added to theobtained paste and was intimately kneaded to form a paint. The obtainedpaint was applied on a cast-coated paper by using a 6-mil applicator,thereby obtaining a coating film thereon.

(4) Heat Resistance:

The heat resistance of the black perylene-based pigment was measured asfollows. That is, the hue values of the black perylene-based pigmentheat-treated in an oven at 200° C. for one hour as well as those of thenon-heat-treated black perylene-based pigment were respectivelymeasured, and the heat resistance of the black perylene-based pigmentwas expressed by the color difference (ΔE) by the same method as used inthe above evaluation of the weather fastness.

(5) Electrical Resistance:

The electrical resistance of the black perylene-based pigment wasexpressed by the volume resistivity value thereof as measured by thefollowing method. First, 0.5 g of the black perylene-based pigment wasweighed and then molded under a pressure of 140 kg/cm² to form a testspecimen. The thus prepared test specimen was set between a pair ofstainless steel electrodes completely isolated from outside by a Teflonholder. The test specimen was applied with a voltage of 15 V by using aWheastone bridge (“TYPE 2768” manufactured by YOKOGAWA DENKI CO., LTD.)to measure a resistance value (R) thereof. After the measurement, anelectrode area A (cm²) and a thickness t (cm) of the test specimen weremeasured, and the volume resistivity value X (Ω·cm) thereof wascalculated from the measured values according to the following formula:X═R/(A/t)

EXAMPLE 1

The compound represented by the formula (I) wherein R¹ and R² both arebutyl group, was heat-treated at 500° C. for one hour in an argon gasatmosphere in a cylindrical heating furnace. The resultant product waspulverized by a ball mill, thereby obtaining a black pigment.

As a result of measuring the X-ray diffraction diagram of the obtainedblack pigment, as shown in FIG. 1, there was observed the diffractiondiagram (as shown in an upper part of FIG. 1), which was different fromthe diffraction diagram (as shown in a lower part of FIG. 1) of thestarting compound. Therefore, it was conformed that the moleculararrangement of the obtained black pigment was changed from that of thestarting compound. Also, as a result of measuring the light absorptionspectrum of the obtained black pigment, as shown in FIG. 2, there wasobserved the absorption spectrum (indicated by the solid line in FIG. 2)exhibiting a broad absorption band covering a still broader visiblelight region as compared to the absorption spectrum of the black pigmentused as the starting material (indicated by the dotted line in FIG. 2).

Further, when the obtained black pigment was heat-treated at 200° C. forone hour, the color difference (AE) was not more than 0.3, and no changein quality thereof was caused. Also, when the black pigment wasirradiated with light for 8 hours using an ultra-high pressure mercurylamp, no change in hue thereof between before and after the irradiationwas observed. As a result, it was confirmed that the black pigment hadan excellent heat resistance and an excellent weather fastness.Essential production conditions are shown in Table 1, and variousproperties of the obtained black pigment are shown in Table 2.

EXAMPLE 2

The same procedure as defined in Example 1 was conducted except that thecompound represented by the formula (I) was replaced with the compoundrepresented by the formula (II) wherein R¹ and R² both are phenylenegroup, thereby producing a black pigment. Essential productionconditions are shown in Table 1, and various properties of the obtainedblack pigment are shown in Table 2. As a result of measuring the X-raydiffraction diagram of the obtained black pigment, there was observedthe diffraction diagram different from that of the starting material.Therefore, it was confirmed that the molecular arrangement of theobtained black pigment was changed from that of the starting material.Also, as a result of measuring the heat resistance, it was confirmedthat the obtained black pigment was thermally stable.

COMPARATIVE EXAMPLE 1

The compound represented by the formula (I) wherein R¹ and R² both arebutyl group, was heat-treated in an oven at 200° C. for one hour. Thehue values of the thus heat-treated black perylene-based pigment and thenon-heat-treated black perylene-based pigment were measured to calculatea color difference (ΔE) therebetween. As a result, it was confirmed thatthe color difference (ΔE) was 1.9 and, therefore, the obtained blackperylene-based pigment was thermally unstable. TABLE 1 Examples andPreparation conditions Comparative Calcining conditions ExamplesCompound used Substituents Temperature (° C.) Atmosphere Example 1Compound of formula (I) R¹ and R²: butyl group 500 Argon Example 2Compound of formula R³ and R⁴: phenylene 500 Argon (II) groupComparative Compound of formula (I) R¹ and R²: butyl group — — Example 1

TABLE 2 Properties of pigment Examples Volume and Blacknes Tinctorialresistivity Weather Heat Comparative s(OD_(min)/ strength value fastnessresistance Examples OD_(max)) (%) (Ω · cm) (ΔE) (ΔE) Example 1 0.57 10510¹¹ <0.3 <0.3 Example 2 0.75 113 10¹¹ <0.3 <0.3 Comparative 0.57 10210¹¹ 1.3 1.9 Example 1

INDUSTRIAL APPLICABILITY

As described above, the black perylene-based pigment according to thepresent invention is a black pigment whose molecule is re-arranged intoa stable phase by heat-treatment, and exhibits an excellent blackness,an excellent heat resistance and an excellent weather fastness as wellas a high electrical resistance and a high safety. Therefore, the blackperylene-based pigment is useful as pigments for inks, paints, ink-jetprinting inks, electrophotographic toners, rubbers and plastics as wellas black matrix materials.

Also, the black perylene-based pigment of the present invention isextremely thermally stable, and is completely free from change in colortone thereof. In addition, since the black perylene-based pigment showsno absorption band in near-infrared and infrared regions, a coating filmcontaining such a black perylene-based pigment has an extremely highreflectivity in near-infrared and infrared regions. In particular, apolyvinyl chloride-based or polyethylene-based coating film containingthe black perylene-based pigment is inhibited from suffering fromtemperature rise even when exposed to sunlight irradiation, resulting inprolonged life of the coating film.

1. A black perylene-based pigment produced by calcining at least one compound selected from the group consisting of compounds represented by the following formulae (I) to (III), at a temperature of 200 to 600° C. in vacuum or in an inert gas atmosphere.

wherein R¹ and R² are identical to each other and are independently butyl group, phenylethyl group, methoxyethyl group and 4-methoxyphenylmethyl group; and R³ and R⁴ may be same or different and are independently phenylene group, alkylphenylene group, alkoxyphenylene group, hydroxyphenylene group, halogenated phenylene group, pyridinediyl group, alkylpyridinediyl group, alkoxypyridinediyl group, halogenated pyridinediyl group and naphthalenediyl group, said R³ and R⁴ being bonded to adjacent positions of the aromatic ring, respectively.
 2. A process for producing a black perylene-based pigment, comprising: calcining at least one compound selected from the group consisting of those compounds represented by the formulae (I) to (III) at a temperature of 200 to 600° C. in vacuum or in an inert gas atmosphere. 